1 <grammar xmlns="http://relaxng.org/ns/structure/1.0"> 2 <start> 3 <ref name="top"/> 4 </start> 5 <define name="empty"> 6 <empty/> 7 </define> 8 <define name="top"> 9 <element name="top"> 10 <choice> 11 <ref name="empty"/> 12 <element name="a"> 13 <text/> 14 </element> 15 </choice> 16 </element> 17 </define> 18 </grammar> 19
